Iowa’s two U.S. senators last week voted against a nominee for deputy energy secretary as part of their fight against the Environmental Protection Agency’s (EPA) consideration of more than 50 petitions for small refinery exemptions, which date back as far as 2011.

The petitions for so-called “gap” filings for waivers threaten to undercut the Renewable Fuel Standard (RFS) and add further pain to farmers and biofuel refiners already hurting from...